Tube equal to one section of a 12AX7?

Pyre · 9th June 2008, 03:46 PM

Is there a 9 pin tube that is equal or very close to one section of a 12AX7?

Thanks

SY · 9th June 2008, 03:57 PM

Why not just use half the tube?

There's a 7 pin single section equivalent with a 6V heater, the 6AV6.

Pyre · 9th June 2008, 04:06 PM

Hi Sy,

Thanks for the info. What I am doing is rebuilding a couple of mono PAM-1 preamps but using the Norman Koren “Spiced” PAS schematic. Each channel uses three 12AX7 half sections. I could use 12AX7’s of course but I was hoping for a lower cost half section equivalent.

oshifis · 9th June 2008, 04:12 PM

~ 6AQ4 (EC91)

SY · 9th June 2008, 04:14 PM

Lower cost? I think it will be more expensive. You're limited to NOS and need twice as many.

High quality 12AX7s are pretty inexpensive. JJ is under $10 brand new.

Pyre · 9th June 2008, 04:25 PM

Yes JJ's cost me about 12 bucks each here plus shipping.

I was hoping that there was something in my stash that was equivalent. When I get home I will check if I have any 6AV6's. I do know that I only have two spare 7 pin sockets.

is there any issue with using both sections of one 12AX7 and half of the second one?

SY · 9th June 2008, 04:30 PM

Nope, no issue, and you might even be able to use that last section to improve the design a bit.

One interesting trick is to only power the heater of one section (i.e., 6V between pin 9 and pin 4 or between pin 9 and pin 5). That prevents the cathode of the unused section from being poisoned, and when the first section wears out, you rewire to use the second section.

jrevillug · 9th June 2008, 04:31 PM

why not use 3 12AX7s? One on each channoel to provide two triodes per channel, and the third to provide a third triode per channel. Crosstalk should be low, despite the sharing.

James

EDIt - I i'm wrong, feel free to shoot me down in flames...

Pyre · 9th June 2008, 04:41 PM

Quote:

Originally posted by SY

One interesting trick is to only power the heater of one section (i.e., 6V between pin 9 and pin 4 or between pin 9 and pin 5). That prevents the cathode of the unused section from being poisoned, and when the first section wears out, you rewire to use the second section.

Thats a great Idea. I have both 6.3v and 12.6v available so it should not be a problem.

SY · 9th June 2008, 04:42 PM

James, for a PAS mod, that works perfectly well. But he's using the PAMs, which are separate mono.

9th June 2008, 03:46 PM	#1
Pyre diyAudio Member Join Date: May 2006	Tube equal to one section of a 12AX7? Is there a 9 pin tube that is equal or very close to one section of a 12AX7? Thanks

9th June 2008, 03:57 PM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX	Why not just use half the tube? There's a 7 pin single section equivalent with a 6V heater, the 6AV6. __________________ "It is not seemly, after wiping your nose, to spread out your handkerchief and peer into it as if pearls and rubies might have fallen out of your head." - Erasmus

9th June 2008, 04:14 PM	#5
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX	Lower cost? I think it will be more expensive. You're limited to NOS and need twice as many. High quality 12AX7s are pretty inexpensive. JJ is under $10 brand new. __________________ "It is not seemly, after wiping your nose, to spread out your handkerchief and peer into it as if pearls and rubies might have fallen out of your head." - Erasmus

9th June 2008, 04:30 PM	#7
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX	Nope, no issue, and you might even be able to use that last section to improve the design a bit. One interesting trick is to only power the heater of one section (i.e., 6V between pin 9 and pin 4 or between pin 9 and pin 5). That prevents the cathode of the unused section from being poisoned, and when the first section wears out, you rewire to use the second section. __________________ "It is not seemly, after wiping your nose, to spread out your handkerchief and peer into it as if pearls and rubies might have fallen out of your head." - Erasmus

9th June 2008, 04:42 PM	#10
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX	James, for a PAS mod, that works perfectly well. But he's using the PAMs, which are separate mono. __________________ "It is not seemly, after wiping your nose, to spread out your handkerchief and peer into it as if pearls and rubies might have fallen out of your head." - Erasmus


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9th June 2008, 04:06 PM	#3
Pyre diyAudio Member Join Date: May 2006	Hi Sy, Thanks for the info. What I am doing is rebuilding a couple of mono PAM-1 preamps but using the Norman Koren “Spiced” PAS schematic. Each channel uses three 12AX7 half sections. I could use 12AX7’s of course but I was hoping for a lower cost half section equivalent.

9th June 2008, 04:12 PM	#4
oshifis diyAudio Member Join Date: Mar 2004 Location: Budapest, Hungary	~ 6AQ4 (EC91)

9th June 2008, 04:25 PM	#6
Pyre diyAudio Member Join Date: May 2006	Yes JJ's cost me about 12 bucks each here plus shipping. I was hoping that there was something in my stash that was equivalent. When I get home I will check if I have any 6AV6's. I do know that I only have two spare 7 pin sockets. is there any issue with using both sections of one 12AX7 and half of the second one?

9th June 2008, 04:31 PM	#8
jrevillug diyAudio Member Join Date: Aug 2006	why not use 3 12AX7s? One on each channoel to provide two triodes per channel, and the third to provide a third triode per channel. Crosstalk should be low, despite the sharing. James EDIt - I i'm wrong, feel free to shoot me down in flames...

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